1. Field of the Invention
The present invention relates to a magnetoresistive head which reads information written onto a magnetic recording medium, and more specifically to a magnetoresistive head of a novel longitudinal biasing method of a ferromagnetic layer for detecting a signal field and the fabricating method.
2. Description of the Related Art
In a magnetoresistive head mounted as a reading element on a magnetic recording and reading device, a GMR (Giant Magnetoresistive) head using a spin valve film having a basic structure of ferromagnetic free layer/nonmagnetic conductive layer/ferromagnetic film fixing layer/antiferromagnetic layer described in Japanese Published Unexamined Patent Application No. Hei 4-358310 is widely used at present. In the magnetoresistive head, in order to inhibit Barkhausen noise, longitudinal biasing must be performed to a ferromagnetic free layer whose magnetization direction is changed by a signal field. As the longitudinal biasing method, Japanese Published Unexamined Patent Application No. Hei 7-57223 describes a method in which a hard magnetic film or a deposited film of a ferromagnetic film and an antiferromagnetic film is arranged at each edge of a magnetoresistive film to set a ferromagnetic free layer on single domain state. The former is called a hard biasing structure which is the mainstream of the current head structure.
The hard biasing structure applies a longitudinal biasing field to a ferromagnetic free layer and is effective for inhibiting Barkhausen noise. On the other hand, it is widely known that magnetization at the edge of an element is fixed to form the so-called insensitive zone. Since the magnetization direction in the insensitive zone is not changed by a signal field, formation of the insensitive zone substantially reduces the reading sensitivity. With the future increase of the surface recording density of a magnetic recording and reading device, the track width is being reduced to increase the occupying percentage of the insensitive zone. This problem is expected to be significant.
To reduce formation of the insensitive zone for the purpose of ensuring the reading sensitivity, the film thickness of a hard magnetic film is decreased to reduce a longitudinal biasing field applied to the ferromagnetic free layer. The effect for inhibiting Barkhausen noise is insufficient. This means that inhibition of Barkhausen noise and reduction of insensitive zone formation are in a trade-off relation which is difficult to satisfy both.
As another means for performing-longitudinal biasing to a ferromagnetic free layer, Japanese Published Unexamined Patent Application No. 2000-173020 describes a longitudinal biasing structure by interface exchange coupling. Since this structure exchange couples the entire surface of a ferromagnetic free layer to an antiferromagnetic layer, it has a reliable and uniform longitudinal biasing effect. In the hard biasing structure previously described, the geometrical arrangement relation between a hard magnetic film and a ferromagnetic free layer and the shape of an element by patterning affect the magnitude of the longitudinal biasing field. On the contrary, in the longitudinal biasing structure by interface exchange coupling, antiferromagnetic material and its film thickness are selected and a suitable exchange coupling field biasing layer is interposed between a ferromagnetic free layer and an antiferromagnetic layer. An advantage of easily adjusting a longitudinal biasing field can be expected. Since an insensitive zone is not formed at the edge of the ferromagnetic free layer, an effective reading track width is increased whereby adaptability to the future track reduction is feared. In addition, since a magnetic pole is caused at the edge of the ferromagnetic free layer, magnetization of the edge is expected to be unstable. A sufficient longitudinal biasing effect cannot be obtained. The influence of this is expected to be significant as the geometrical track width is being reduced.